1. Field of the Invention
The present invention relates to an IC socket which comprises a socket body, a cover and a plurality of contacts and performs electrical engagement and disengagement of said contacts with the leads of an IC package, and, more specifically, an improvement of contact reliability of the IC socket concerned.
2. Description of the Prior Art
Generally, all IC packages are subject to screening inspections in several methods to ensure their original functions. One of these screening inspections of the IC packages is a burn-in test, which is intended to test high temperature characteristics of IC packages by setting the IC packages mounted on IC sockets in a convective oven and actuating them in a high temperature environment.
FIGS. 15 to 18 respectively show an IC socket applicable to an automatic machine for use in the burn-in test disclosed in the U.S. Pat. No. 4,886,470. More specifically, FIG. 15 is a perspective view showing a normal condition before the screening inspection. FIG. 16 is a cross sectional view showing the IC socket on which an IC package is mounted. FIG. 17 is a cross sectional view showing the operating condition and FIG. 18 is a load-displacement characteristic view of the contacts.
This IC socket comprises a socket body 1', a cover 2' and a plurality of contacts 3' as shown. This plurality of contacts 3' respectively have a contact portion 31' for electrical engagement with a lead L of the IC package P, a cantilever portion 32' for rotating this contact portion 31' to allow electrical disengagement of the lead L from the contact 3', and an engaging portion which slides to engage with the cover 2'. In this case, when the cover 2' is depressed downwardly against the resilience (repulsive force) of the contacts 3', the contacts 3' are forcibly displaced outwardly and the contacts 3' and the lead L of the IC package P are released from electrical engagement. Under this condition, therefore, the IC package P can be remounted. When a force for depressing the cover 2' is removed, the contacts 3' are turned around in a opposite direction to the aforementioned direction and connected again with the lead L of the IC package P.
However, in the above-described IC socket, an engaging force between the contact and the lead (L) has been obtained as a resilient repulsive force which would cause the contact to be displaced by as much as the thickness of the lead (L) as shown in FIG. 16 and therefore, if the IC package (P) having the leads (L) with a different thickness is used, a variation in the thickness of the lead (L) has greatly affected the engaging force and a stable engaging force could not be obtained and consequently a stable electrical contact resistance could not be obtained. In addition, there has been a problem that an error of thickness of the leads (L) resulting from manufacturing affects significantly effects the electrical contact resistance. Accordingly, to obtain a stable engaging force, that is, a stable electrical contact resistance, it has been necessary to change the resilience of the contact 3' in accordance with the thickness of the lead (L) of the IC package (P) or partly change the shape of the contact 3' and the socket body 1' and moreover prepare various IC sockets to meet variations in the thickness of the lead (L).
An object of the present invention which was made in view of the above problems is to provide an IC socket capable of providing a stable engaging force in response to variations in the thickness of the lead (L) of the IC package (P).